1. 11/8/2000 1 Plasma Assisted Surface Modification: Low Temperature Bonding SFR Workshop November 8, 2000 Yonah Cho, Adam Wengrow, Chang-Han Yun Nathan Cheung Berkeley, CA 2001 GOAL: to establish plasma recipes and adhesion data for Si, oxide and metal surfaces by 9/30/2001.

2. 11/8/2000 2 Motivation SiO 2 SOI Si SOI LEDs on Si Silicon-On-Insulators Dual Gate MOS Micro Cavities 200  m

3. 11/8/2000 3 Bonding Methods & Temperature Dependence Hydrophobic Si Hydrophilic Si 3000 2500 2000 1500 1000 500 0 100 200 300 400 500600 700 800900 Bonding Energy (mJ/m 2 ) Annealing Temperature ( o C) Bonding Energy vs. Temperature Anodic Bonding Anodic Bonding Direct Bonding Direct Bonding Metal Bonding Metal Bonding Adhesive Bonding Adhesive Bonding Choice of bonding method depends on thermal budget & materials systems

4. 11/8/2000 4 Plasma Treatment Gases Used: O 2, He, N 2, Ar Pressure 200mTorr Power 50W-300W Time 15-30 seconds + O2O2 Thermal Annealing Room Temp Bonding Chemical Cleaning: Piranha + RCA - Bonding Schematics

5. 11/8/2000 5 Bonding Kinetics Temperature ( o C) 50 100 200 1000/Temperature (K) Si-Si O 2 Plasma-treated Si-Si Chemically cleaned Si-Si Chemically cleaned SiO 2 -SiO 2 E a ~ 0.07 eV E a ~ 0.2 eV E a > 0. 7 eV Plasma treated Si surfaces achieve covalent bonding as low as 105 o C O 2 Plasma-treated Si-SiO 2

6. 11/8/2000 6 115 Binding energy (eV) Surface Chemistry: XPS SiO 2 Si Hydrophobic Si Hydrophilic Si O 2 plasma treated Si Thermal SiO 2 SiO 2 Si

7. 11/8/2000 7 Surface Morphology Chemically cleaned Si O 2 plasma 150W-300W 30 seconds No Change in Surface Roughness RMS < 0.5 nm

8. 11/8/2000 8 Surface Modification by Concomitant/Sequential Plasma Treatment Mechanical and chemical properties of surface can be effected. Modified surface layer can be from substrate or grown / deposited / transferred layer. Physical and/or chemical changes of surface possible by altering chemical composition of plasma and ion energies. Surface Layer Si Substrate Plasma Treatment Modified Surface *By simply varying the potential of the PIII reactor, it can serve as surface modifier to implanter.

9. 11/8/2000 9 2002 and 2003 Goals Demonstrate concomitant plasma treated deposition layer as effective diffusion layer by 9/30/2002. Demonstrate polymer surface modification with plasma implantation by 9/30/2003. Project summaries & publications are available at http://plasmalab.berkeley.edu